Client
and Server Look-up Tables

Each
ADDE client command starts a transaction by requesting data from a server.
Both the client and server must recognize the command's specified dataset name
in their look-up tables. On the client, this table is called the routing
table because it determines which server to route the data request to.
On the server, this table is called the mapping table because it maps
the group and descriptor to a specific image, grid, point, navigation or text
dataset.

Client
Routing Table

The client
routing table contains two lists: a list of group names with their associated
server IP addresses, and a list of aliases with the dataset names they represent.
When you enter an ADDE command, the client routing table is scanned for an
entry with the specified group name or alias. If an entry is found, the data
request is routed to the server specified in the entry. If the group name or
alias is not found in the client routing table, the request is routed to the
local server.

Use the DATALOC command
to manage the list of group names. Use the AKA command
to manage the list of aliases. Aliases allow you to use a short, easily remembered
name to represent a dataset name in other ADDE commands. You can use this alias
regardless of which server the dataset is stored on. For example, you could
create the alias GV to represent the dataset name SSEC-RT/GOES-VIS-GLO.

Each user can
access multiple client routing tables. This optional feature is useful when
a site table has the default routing information and alias names for all users
and each user has a local table with individualized routing information and
alias names. The default file for your local table is MCTABLE.TXT.
The site table, if it exists, is maintained by your site administrator or operations
staff and is usually write-protected so you can't modify it. You may have to
NFS mount its directory to access the file. Use the DATALOC and AKA commands
to list information from all the client routing tables accessible to you.

If you decide
to use multiple client routing tables, you must set the Unix environment variables MCTABLE_READ and MCTABLE_WRITE.
The MCTABLE_READ value specifies,
in order of precedence, the client routing tables accessed when searching for
a group or alias match. The tables must be separated by semicolons (;) and
specified as either file names or fully qualified path names (directory and
file name). The MCTABLE_WRITE value
specifies the single client routing table you can modify by creating or deleting
group or alias entries with the ADD and DEL parameters of the DATALOC and AKA commands.

You cannot
specify more than one table in MCTABLE_WRITE.
SSEC recommends that the table you specify be the same as the first table in MCTABLE_READ.
See the appropriate example below for your system.

McIDAS-X Example

If you want
to use $HOME/mcidas/data/MCTABLE.TXT for
your local table and /data/ADDESITE.TXT for
your site table, enter the following Unix commands (substitute the equivalent if using C shell) to set the environment variables.

If you want
these values for MCTABLE_WRITE and MCTABLE_READ set
each time you login to your account, add the commands above to your $HOME/.mcenv file
and add the following line to your $HOME/.profile (ksh) or $HOME/.cshrc (csh) file.
Be sure to leave a space between the period (.) and $HOME.

. $HOME/.mcenv

Server
Mapping Table

The
server mapping table maps dataset names to the files that make up the datasets.
When the server receives a data request from a client, it reads the mapping
table to locate the correct dataset. The server sends the requested data back
to the client so it can list or display the data.

Use the DSSERVE command
to list or modify the server mapping table. Clients can only modify their local
server's mapping table; they cannot modify a remote server's mapping table.
The remote server's administrator must inform the client's administrator or
user which ADDE group names the client may access. The client's administrator
then modifies the client routing table with command DATALOC so
applications can request data from groups located on the remote server.